1. Field of the Invention
The present invention relates to a magnetron which is an electron tube generating microwaves, and a method of adjusting a resonance frequency of the magnetron.
2. Description of the Related Art
A magnetron is used as a high frequency generation source in an electric apparatus using microwaves, such as a microwave heater or a microwave discharge lamp. A magnetron is configured to include a vacuum tube portion disposed at the center thereof; a cooling portion located on an outer circumference of the vacuum tube portion; a pair of annular magnets disposed on the same axis as the vacuum tube portion; a yoke magnetically coupling the annular magnets; and a filter circuit portion. There are magnetrons which operate, for example, at fundamental frequencies of 2450 MHz and 915 MHz.
A resonance frequency of a magnetron is determined in a stage in which an anode cylinder, a tabular vane, and a pressure-equalizing ring (strap ring) are fixed. In a case where a resonance frequency is desired to be adjusted, there is a method or the like of adjusting a resonance frequency by striking and distorting the pressure-equalizing ring after fixing. The method of distorting the pressure-equalizing ring cannot be said to be a favorable method in terms of reliability, and may cause deterioration in characteristics depending on a distortion amount. In a case of a hard pressure-equalizing ring or a thick pressure-equalizing ring, it is hard to distort the ring, and thus a resonance frequency cannot be easily adjusted.
PTL 1 discloses a magnetron including an anode cylinder and a plurality of tabular vanes disposed radially in the anode cylinder, in which the tabular vanes are alternately connected to each other via a pressure-equalizing ring, and the magnetron has structure in which a protrusion facing the pressure-equalizing ring which is not connected to a tabular vane is provided at the tabular vane, and the protrusion is deformed so that a capacity between the tabular vane and the pressure-equalizing ring which is not connected to the tabular vane is changed, and thus an oscillation frequency is adjusted.